Method for treating leather



2,824,815 Patented Feb. 25, 1 958 ice METHUD FOR TREATENG LEATHER Ian C.Somervilie, Willow Grove, and Richard F. M. Fisher, Jenkintown, Pa.,assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation ofDelaware No Drawing. Application May 13, 1954 Serial No. 429,704

19 Claims. (Cl. 117-1355) This application is concerned with improvedmethods for the impregnation of leather, and is particularly concernedwith an improved method for imparting waterrepellent properties toleather and especially without objectionably decreasing the permeabilityof the leather to water vapor.

Up to very recent times, the most common method of making leatherresistant to water consisted in stufling, i. e., drumming emulsions ofwax or grease into the tanned skins prior to drying down. When this isutilized in making shoe upper leather, it is found that although thisshows good repellency to water in a static test, serious leakage takesplace soon after the leather is flexed repeatedly such as in the flexingthat occurs across the vamp in walking. Moreover, the presence of thewax or grease in the interstices between the fibers seriously reducedthe water vapor permeability of this leather, making the shoesuncomfortable in warm weather, while solidification at low temperaturesmakes these shoes stifi and less flexible under winter conditions.

A considerable improvement was effected recently when oil-in-wateremulsions of various water-insoluble organic polymers were applied topartially fatliquored shoe upper leather, and then broken by change inpH value, brought about either by reaction with the leather itself or bythe addition of an organic acid or by a combinaticn of these factors.This also resulted in deposition of the polymer largely in the spacesbetween the fibers, but in this case it has been claimed that 50% of theoriginal water-vapor permeability is retained while the water repellencyunder dynamic conditions is greatly improved over that for the customarystuffed shoe leather. Parallel experiments on glove leather have beenstated to produce comparable results on chrome tanned horse fronts.

The introduction of water-insoluble compounds into leather by dissolvingthem in a suitable non-aqueous solvent has been known for a considerableperiod. In this way better penetration is frequently effected and theorganic materials tend to coat the surface of the fibers rather than bedeposited in the interstices between the fibers. Probably one of themain reasons why it has not been more widely used in commercial practiceis an economic one; namely, that it is much more expensive to useorganic solvents than it is to operate in an aqueous medium. One of thefactors in this higher cost is that high concentrations of theimpregnant have to be used.

, Most of the impregnant remains behind in the large ex cess of solventin which it is readily soluble, because it has little affinity in thismedium for the leather fibers with which it is in contact.

In accordance with the present invention, a hydrophobic impregnant,preferably of a waxy or resinous material of viscous or plasticcharacter, is dissolved in a hydrophobic organic solvent selected fromthe class of hydrocarbon and chlorinated hydrocarbon solvents, and theleather is agitated within the solution until an equilibrium conditionof distribution of the impregnant between the solvent and the leather issubstantially obtained. A hydrophilic water-soluble solvent having somemiscibility with the initial hydrophobic solvent and which reduces thesolubility of the impregnant in the solvent system is then addedgradually or in periodically repeated doses to favor the deposition ofthe impregnant within the leather and the leather is further agitated toexhaust the impregnant from the solution. The hydrophilic solventcomprises at least a predominant proportion of organic solvent materialand may contain water. The hydrophilic solvent must have somemiscibility with the hydrophobic solvent and the impregnant must havemuch less solubility in the hydrophilic solvent than in the initialhydrophobic solvent. it has been found that this system of operationthoroughly impregnates the leather and distributes the impregnantsubstantially uniformly on the fibers of the leather withoutobjectionably decreasing the permeability of the leather to moisturevapor. After sufiicient exhaustion in this manner, the leather isremoved from the solution, drained, and dried.

In practice, the procedure of the present invention is performed upon atanned leather in air-dry condition after dyeing and fatliquoring, butpreferably after only a portion of the normal fatliquor that iscustomarily given. After the treatment with the impregnant, the leathermay be subjected to a prolonged treatment at elevated temperatures forthe purpose of curing the impregnant if it is of a nature to be furtherpolymerized, condensed or both polymerized and condensed to an insolubleand/or infusible condition. The leather may also be subjected to theusual subsequent treatment-of lacquering or finishing in other waysdepending upon the purpose for which the leather is intended. In mostcases, however, the treatment with the water-repellent impregnant is thefinal treatment of the leather. If there is no objection to water vaporimpermeability in the leather because of the use to which it is intendedto be put, the leather which is to be impregnated in accordance with thepresent invention may have been previously treated by a so-calledstufling procedure. However, the present invention is primarily directedto the making of leathers which are intended for use as gloves, shoes,garments, and the like waterrepellent without objectionable loss inwater-vapor permeability and stufiing or equivalent processes are notcontemplated in these cases.

The first step in the process of the invention involves the preparationof a solution of the hydrophobic impregnant or water-repellent materialin the hydrophobic solvent. The volatile solvent used may be ofaromatic, naphthenic or aliphatic hydrocarbon type, such as benzene,toluene, Xylene, cyclohexane, tetrahydronaphthalene,decahydronaphthalene, turpentine, solvent naphthas, mineral thinners,high flash point naphthas that are frequently referred to as safetysolvents, light kerosene, or chlorinated hydrocarbons, such as ethylenedichloride, chloroform or carbon tetrachloride. The solvent may be amixture of several of the above mentioned solvents. The concentration ofthe impregnant within the solution may be from 1% to 15% by weight andit may even approach the saturation limit at the temperature ofoperation. In some cases, the viscosity of the resulting solution mayrequire the concentration to be kept within the lower part of the rangespecified above, but even at the lower concentrations the method of thepresent invention effects a thorough impregnation and substantiallyuniform distribution of the impregnant within the leather structure. Theamount of the impregnant used in the bath or solution which is appliedto the leather may amount to from 1% to 60% by weight of the leather,and for most practical purposes the preferred amount is from 5% to 20%by weight of the leather. The bath ratio, by which is meant the ratio ofthe weight of the solution to the weight .of the dry leather, may be Ivent medium.

-. r 2, 24,810 r a r from 2:1 to :1 and it is preferred that this bathratio be from 4:1 to 6:1.

The leather is agitated within the solution of the impregnant at anytemperature from room temperature up to about 65 C. The temperature ofoperation should be appreciably below the boiling point of thesolvents'used. Generally, it is preferred tooperate at temperatures fromroom temperature to 50 C. The agitation of'the leather total weight ofthe mixed hydrophilic solvent to reduce V the solubility of theimpregnant in the resulting solvent 7 system. Further improvement isgenerally obtained as within'the solution may be effected in. the typeof drums 1 customarily used in tannery practice for tanning 'or,fat-

liquoring in whichthe drums are rotated to efieet tumbling of theleather within the solution. Of'course, any other equipment that willeffect agitation of the leather within the solution without harming theleather'may be employed. For example, this agitation may be efiected byrepeated dipping of the leather into the impregnating bath.

The agitation or tumbling of the leather within the solution is carriedon for a period of time which is suflicient to effect thoroughimpregnation and distribution. This time may vary: from about one-halfto three or four hours in order to bring the system substantially to anequilibri- 'um condition of distribution of the impregnant betweengradually or in portions at successive intervals. As stated previously,the hydrophilic solvent must have some miscibility with the initialhydrophobic solvent and the impregnant should be substantiallyinsoluble'in the hydrophilic solvent or it must have much lesssolubility therein than in the initial solvent. Sufiicient hydrophilicsolvent is added to markedly reduce the solubility of the impregnant inthe resulting solvent medium, and the amount ofhydrophilic solventrequired to bring about .this condition may be from 3% to 150% by weightof the initial solvent; preferably from 20% to on the weight of theinitial solvent is added. The amount depends on the particularhydrophobic solvent and the particularhydro ing about a precipitation ofthe impregnant withinthe sol- In the preferred operation, sufiicient ofthe hydrophilic solvent is added to separate the system into two liquidlayers or phases, one of which is primarily a hydrophobic layer and theother is primarily'a hydro philic layer. The hydrophilic solventemployed may be a lower alcohol, such as methyl, ethyl, n-propyl,isopropyl, n-butyl, or isobutyl alcohol, ethylene glycol,{diethy1eneglycol, the methyl or ethyl monoethers of ethylene glycol or diethyleneglycol, acetone, dioxane, methyl ethyl ketone, methyl acetate, ethylacetate, or a mixture of two or more of theseindividual solvents,including particularly a mixture of one or more of these organicsolvents with water. 7 a

The hydrophilic solventemployed in any particular instance depends uponthe particular impregnant used therein and its solubilitycharacteristics. Generally, a hydrophilic solvent is selected in whichthe impregnant has markedly lower solubility lthan'in the hydrophobicsolvent initially used. In addition, water can be added to a hydrophilicorganic solvent or a mixture thereof to provide a mixed hydrophilicsolvent in which the. impregnant has even lower solubility than in the.straight organic hydrophilic solvent. For example, when the simplemonohydric alcohols mentioned hereinbefore are used with the preferredacrylic polymer impregnants described hereinafter, it is generallypreferred to add water in. an amount of at least about 3% by weightbased on the the water is increased in proportion up to about 25% to 30%by weight and in some instances to even higher proportions. Even inthose systems in which the impregnant is of reduced solubility inanindividual hydrophilic organic solvent, water may be present in amountsof 3% by weight or more with.somewhatimprovedldeposition of theimpregnant on the leather and corresponding better exhaustion of theimpregnating system. Aspointed out a above, in preferred instances,suflicient hydrophilic solvent is added to effect a separation into twoliquid layers which facilitates the recovery of impregnant and/ orsolvents from the spent liquor system. Those systems in which at least3% of water is present in the hydrophilic solvent frequently produce aseparation into two liquid layers or phases and they are accordinglypreferred for this additionalreason. However,suchseparationalso occurseven with other hydrophilic solvent systems which do not contain water.when the hydrophilic solvent is used in an amount which exceeds itslimit of miscibility in the hydrophobic solvent. During the addition ofthe hydrophilic solvent, or after 7 each addition of a portion thereof,the agitation of the, leather is continued within the liquid system.After the completion of the addition of the hydrophilic solvent or aftereach addition when several aremade, the agitation is effected for aperiod of time 'sufficient'to bring the system to a new equilibriumcondition inrespect to the distribution of the impregnant between theleather and either the solvent system or the hydrophobic, layer of thesolvent system, if two layers or liquid phases form. This may; involvecontinued agitation for a period of about one-half to three hours totaltime after the start of the addition of the hydrophilic solvent to thesystem. f

After completion of the agitation within theliquid system, the leatheris removed from the liquid, drained and philic solvent that are mixed aswell as on the particular 7 dried. When the impregnant is of athermosetting character the drying may serve to cure the impregnant toits final condition of polymerization or condensatiomor, if. desired,continued heating maybe carried out beyond the completion of drying tobring about the final-condition of polymerization or condensation of theimpregnant within the leather. i

The impregnant that maybe applied to leather for effecting the treatmentmay be any hydrophobic material which, in its final condition in theleather imparts to the leather an essentially flexible character atroom'ternperature and at all other normal conditions of use. For thispurpose, Waxy or resinous materials of hydrophobic character are useful.For example, the waxes consisting of long-chain saturated hydrocarbonshaving from 14 to 30 carbon atoms, such as parafiin. waxes, may be used.Waxy materials of ester types,such asthe esters ofnatural or syntheticorigin of long-chain saturated aliphatic 1 acids and/ or of saturatedaliphatic'alcohols having from 8 to 30 carbon atoms are also included.Examples of such esters are beeswax, carnauba wax, tallow, mo ntan Wax,wool fat, stearyl acetate, Similarly, waxy esters of polyhydric alcoholsother than glycerol may be used. Examples are the esters of erythritol,hexitans or hexides which are substantially. completely esterified withsaturatedfatty acids,e. g., sorbidef distearate, sorbitantetrapalmitate, mannidedipalmitateg and so forth. Similar waxy esters'ofaliphatic dicarbox-f,

ylic acids with long-chain alcohols containing 8 m 18 and h up to 30 ormore carbon atoms are useful. Examples are. di-n-hexadecyl succinate,di-n-dodecyl succinate, di-n-f octadecyl succinate, diesters ofn-octanol, n-decanol, n-

dodeca nol, n-hexadecanol, and n-octadecanol wit hn hexylsuccinic acid,n-heptylsuccinie-acid,'n-octylsuccinic V ethylene glycol stearate.

atoms, such as octyl isocyanate, decyl isocyanate, dodecyl isocyanate,undecyl isocyanate, hexadecyl isocyanate, octadecyl isocyanate, montanylisocyanate.

Another type of hydrophobic impregnant includes the longchain ketenessuch as d-odecyl ketene, hexadecyl ketene, and octadecyl ketene.Similarly, long-chain ketones, such as dodecylmethyl ketone anddi-dodecyl ketone may be used. Long-chain amides, such as stearamide,may be employed.

Various polymeric resinous materials may be applied to leather by theprocedure of the present invention, such as various types of silicones,including the organo-polysiloxanes, such as the methyl polysiloxaneresin intermediate, methyl-phenyl poly-siloxane resin intermediate, orethylphenyl polysiloxane intermediate of Examples 1 to 6 of U. S. Patent2,389,477.

Other hydrophobic polymeric resinous materials that may be used includethe water-insoluble polymers obtained by the polymerization of one ormore monoethylenically unsaturated materials, such as ethylene, vinylchloride, vinyl bromide, vinyl fluoride, vinyl esters of long-chainfatty acids, such as lauric, myristic, palmitic, and stearic acids;homopolymers of ureido esters of acrylic and methacrylic acids havingthe general formula CH C R) CO O-ANHCONH where R is methyl or hydrogenand A is an alkylene group having from 5 to 14 carbon atoms; esters ofacrylic, methacrylic, or itaconic acids with long-chain alcohols,

e. g., octyl, decyl, undecyl, lauryl, myristyl, hexadecyl,

and octadecyl alcohols including (a) copolymers thereof with 2% to 95%of other monoethylenically unsaturated copolymerizaole materials whichalone would produce hydrophobic homopolymers, such as styrene, vinylacetate, and esters of acrylic, methacrylic or itaconic acids with loweralcohols having from 1 to 7 carbon atoms, especially the methyl, ethyl,isopropyl, and butyl esters of acrylic, methacrylic and itaconic acids,and ureido esters of acrylic and methacrylic acids having the generalformula where R is methyl or hydrogen and A is an alkylene group havingfrom 5 to 14 carbon atoms and (b) copolymers thereof with 1% to 15% ofother monoethylenically unsaturated copolymerizable monomers which alonewould produce hydrophilic homopolymers such as acrylic acid, methacrylicacid, itaconic acid, and ureido esters of acrylic and methacrylic acidshaving the general formula CH =C R) COOBNHCONH where R is methyl orhydrogen and B is alkylene group having from 2 to 4 carbon atoms, suchas fi-ureidoethyl I methacrylate, /3-ureidoethyl acrylate,

CH =C CH COOCH CH CH NHCONH and CH =CHCOOCH CH(CH )NHCONHWater-insoluble polymers of monoethylenically unsaturated moleculescomprising at least 50% by weight of at least one ester of acrylic,methacrylic, or itaconic acids with higher saturated fatty alcoholshaving 8 to 18 carbon atoms are preferred impregnants because of their Yhigh degree of hydrophobicity, their flexibility at low temperatures,such as are encountered in Arctic regions,

the penetration of the leather structure by the solution. Generally, thedegree of polymerization should not be so high that solutions of 30% ofthe polymer in the selected hydrophobic solvent, such as toluene, areover 1000 centistokes at F.

The procedure of the invention may be applied to all types of leatherintended for all sorts of uses. It is particularly important for garmentleathers that are intended to be used as wearing apparel, such as shoes,gloves, caps and jackets. The leather treated by the invention isoutstanding in respect to its combined properties of being highlywater-repellent, and at the same time highly permeable to water vapor.Because of these characteristics, gloves, shoes, and the like can beworn without discomfort since their vapor permeability allows them tobreathe while their waterrepellency hinders the transmission of liquidwater therethrough. In addition, the procedure of the present inventionis so effective in uniformly and thoroughly distributing thewater-repellent materials within the fibers of the leather structurethat the impregnated leathers retain their water-repellency through longperiods of normal flexure. The leather treated by the present inventionalso shows good scuff-resistance and general wearing qualities.

The procedure of the present invention is applicable to leathers thathave been tanned in any way whatsoever, such as by a chrome tannage, analum tannage, vegetable tannage, a zirconium tannage, a synthetictannage as well as to leathers which have been retanned.

In the examples which follow and are illustrative of the invention, theflexing test for measurement of waterrepellency under dynamic testingconditions is a modification of that developed by Maeser as adopted asthe Federal Specification for estimation of water penetration designatedKKL-3lla; methods 8021 and 8031. This test method was modified in that aleather sample having a size of 4%" by 4% was used and in that, insteadof the chamois wick, pieces of weighed cotton were placed in the troughafter initial penetration of water had occurred, and these pieces werechanged at 250, 500, 750, 1000 and 2000 flexes and the sum of the gainin weight taken as Water Transmitted. At the end, the increase in weightof the leather sample, after wiping ofi excess surface water, was takenas Water Absorbed, the Total Water being that absorbed plus thattransmitted.

Example 1 (a) Twenty pounds of a copolymer (obtained by thepolymerization of a mixture of about 1 part by weight of cetylmethacrylate and about 2 parts by weight of stearyl methacrylate andhaving a viscosity of 520 centistrokes in toluene at 30% concentrationand at l00 F.) were dissolved in 400 pounds of a mineral thinner(essentially an aliphatic hydrocarbon mixture of boiling point rangefrom 300 to 390 F.). Chrome-tanned horse fronts (100 pounds), which hadbeen given 10%, that is one-half the normal amount, of fatliquor forglove leather, were taken in the dry condition after staking and drummedin the mineral thinner solution. After three hours tumbling in the drum,10% by volume (based on the initial solvent) of isopropyl alcohol(containing 10 parts water by olnme per 100 parts) was added and thetumbling in the drum was continued for one-half hour. Two furthersimilar additions were then made at one-half hour intervals, drummingbeing continued throughout and for one-half hour after the lastaddition, the skins were removed, allowed to drain and then hung in awarm room fill- F.) for 48 hours. After cooling to room temperature andtaking out, the dry leather was found to have a soft, mellow feel. Ithad retained its original color and appearance and was free fromstickiness and unpleasant odor. On subjection to the modified Maesertest above, it was found to withstand 5000 flexes to the First Leak andthe Total Water amounted to one gram.

(b), In similar fashion, ehromertanned horse fronts of thesamejcharacter were drummed in 400% of a mineral.

thinner solution of the copolymer containing one'part by ;weight of thecopolymer in seven parts by weight of the.

. 'tirne a total of one gram of water was obtained. Comparable test runs'on thesame type of glove leather without impregnation with thecopolymer gave values of 500 flexesto the First Leak and a large valueof about 120 grams Total Water. 1 It thus appears that the specialmethod of application imparts improved water-repellency when tested.nnder dynamic conditions even when the initial concentration of thewater-repellent impregnant within the initial hydrophobic solvent isonly about 4 to 5% as compared to a concentration of 12.5% whenimpregnation is effected without the subsequent introduction ofhydrophilic solvents.

(c) Polymers of lauryl methacrylate, octyl acrylate, lauryl acrylate,'myristyl acrylate, homopolymers of CHFC(CH )COO(CH NHCONHz, and alsocopolymers 015 95 octyl acrylate with 5% S-ureidoethyl methacrylate, 85%cetyl acrylate with 15% fi-ureidoethyl;

acrylate, 9 lauryl acrylate with 10% of CHZ;C(CH3)COOCH2CH(CH3)NHCONH2and 25% decyl a'crylate with 75% cH,=c cH cootcup ivncoi-nv were appliedto chrome-tanned horse fronts by the procedure of paragraph (a) above.The resulting leathers showed excellent resistance to transmission ofliquid water while remaining highly permeable to water vapor.

V 7 Example 2 V I (a) Chrome-tanned horse fronts in air-dry conditionwere treated with 20% of the same polymer in mineral thinner asdescribed in Example 1 (a). In this case, however, 10% (by volume of theinitial solvent) of isopropyl alcohol, containing '30 parts 'water (byvolume) per 100 parts; was then added and'drumming continued for onehalfhour. Two further similar additions'were then made and drummingcontinued one hour, after which the skins were processed as described inExample 1. In testing as before, these leathers showed nearly4000 flexesto First.

Leak and almost grams Total Water.

(b) The same procedure was followed except that only of the polymerwasused. The leather showed 3000 flexes to First Leak and 8 grams TotalWater.

' Example 3 Chrome-tanned horse fronts in air dry condition were treatedwith of the same polymer in mineral thinner as described in Example1(a). In this case, however, 10% (by volume of the initial solvent) ofmethoxyethanol was added and drumming continuedone-half hour. Onefurther similar addition was made and drumming continued one hour; thenskins were removed and processed as usual. In testing forwater-repellency these leathers showed over 5000 flexes to First Leakand 1 grams Total Waterv j a f Example 4 Chrome-tanned horse fronts indry condition were treated with 20% of the copolymer of Example 1 (a) ina solution containing 45% mineral oil and 500% toluene, all percentageson dry skin weight. After drumming for 4 hours, 3% (by volume of theinitial solvent) of isopropyl alcohol, containing 4 parts water (byvolume) was added, and drumming continued one-half hour. Two

r at half-hour intervals, drumming beingcontinued throughfurther similaradditions were made at half-hour intervals Example 5 Dry chrome-tannedheavy duty cowside glove leather was drummed with 400% (on the leatherweight) of a mineral thinner solution of 10% (on the leather weight) ofoctadecyl isocyanate. After drumming three hours,

25% (by volume of initial solvent) of isopropyl alcohol 7 containing 10%water by'volume was added in five feeds out and one hour after the finaladdition. On removal,

draining and drying in a Warm room 48,hours, theMaeser test showed17,500 flexes before First Leak and .Total' Water of 2 grams. Withoutaddition of the hydrophilic solvent, the test showed only 2500 flexesbefore First Leak :andTotal Water of 4 /2 grams.

Example ,6

Dry chrome-tanned horse front glove leather was drummed with 400% (onleather weight) of a mineral V five feeds at half-hour intervalsdrumming being continued throughout and for one hour after the finaladdition. removal, draining and drying in a warm roomj48 hours, theMaeser test showed 13,000 flexes before First Leak and Total Water of 2grams. Without addition of the hydrophilic solvent, the test showed only1000 flexes before First Leak and Total Water of 17 grams.

Example '7 Dry chrome-tanned horse front" glove leather 'was drummedwith 500% (on leather weight) of a' solution in a blend of 5 partsmineral thinner and 3 parts carbon tetrachloride of 10% (on leatherweight) of octadecylketener After drumming 3 hours, 50% (by volume ofinitial solvent) of isopropyl alcohol containing 10% water by volume wasadded in five feeds, drumming being continued throughout andone hourafter the'final addition. On removal, draining and drying in a war'mroom'48 hours, the Maeser tested showed 4700 flexes before First Leak andTotal Water of 1 gram. Without addition of the hydrophilic solvent, thetest showed only 440 flexes before First Leak and 46 grams of TotalWater.

Example 8 Dry 7. chrome-tanned horse front glove leather was drummedwith 400% (on leather weight) ofa solution in mineral thinner of 20% (onleather weight) of the co-:

polymer of Example 1(a) and 2% (on leather weight) of the silicone ofExample 6. After drumming 3 hours, 50% (byvolume of initial solvent) ofisopropyl alcohol before First Leak and Total Water of 1 /2 grams.

showed only 1000 flexes and 4 /2 grams Total Water.

Example A dry chrome tanned ,deerskin for glove or garment V 7 leatherwas drummed with 400% of a solution in mineral thinner of 20% of thecopolymer of Example 1(a) and 2% of the silicone of Example 6. In thiscase, 10%

(by volume of initial solvent) of isopropyl alcohol, con-. taining 30parts water (by volume) per parts, was

added and drumming continued one-half -l 1our. Two

further similar additions were made at half-hour intervals and drummingcontinued throughout and one hour after the last feed; then the skinswere removed and processed as usual. In testing for water-repellency,the leather was flexed over 40,000 times and the testing was stoppedbefore any leaking occurred; at the time testing was stopped, it showedonly 1% grams of Total Water.

Example A dry, stuifed army retan side leather (which is a chrome-tannedleather heavily retanned with vegetable ex tract) was substituted forthe chrome-tanned horse fronts and carried through the process ofExample 1(a). The resulting leather, while not nearly as water-repellentas straight chrome-tanned leather, on testing, showed three times asmany flexes to First Leak and half the amount of Total Water that thesame leather showed without treatment with the copolymer.

Example 11 Dry chrome-tanned horse fronts were treated with of beeftallow in a solution containing 400% mineral thinner. After drumming 3hours, 150% (by volume of initial solvent) of iscpropyl alcoholcontaining 10% water by volume was added in eight feeds at 20-minuteintervals, drumming being continued throughout and /2 hour after thefinal addition. On removal, draining, and drying in a warm room 48hours, the Maeser test showed 2,500 flexes before First Leak and TotalWater of 1.5 grams. Without addition of the hydrophilic solvent, thetest showed only 630 flexes before First Leak and Total Water of 50grams. The untreated leather showed 590 flexes before First Leak andTotal Water of 66 grams. (All values are averages of three tests.)

Example 12 Dry chrome-tanned horse fronts were treated with 20% ofcarnauba wax in a solution containing 1000% of carbon tetrachloride.After drumming 3 hours, 54% (by volume of initial solvent) of isopropylalcohol containing 10% (by volume) of water was added in six feeds at20- minute intervals, drumming being continued throughout and /2 hourafter the final addition. On removal, drain- A ing, and drying, theMaeser test showed i200 fiexes before First Leak and Total Water of 2.5grams. Without ad dition of the hydrophilic solvent, the test showedonly 1000 flexes before First Leak and Total Hater of 48 grams whereasthe untreated leather showed 590 flexes sisting of volatile organicsolvent and aqueous solutions of volatile organic solvents comprising atleast a predominant proportion of organic solvent in which theimpregnant has substantially less solubility as compared to thehydrophobic solvent while continuing the agitation until additionalimpregnation is effected, removing the leather from the liquid system,draining it, and drying it.

2. The method of impregnating leather comprising agitating the air-dryleather with 200% to 100070, on the weight of the leather of a solutionin a volatile hydrophobic organic solvent medium of 1% to 50% on theweight of the leather of a hydrophobic impregnant until substantialimpregnation is effected, adding 3% to 150% by volume, based on thevolume of initial solvent, of a watersoluble hydrophilic solventselected from the group consisting of volatile organic solvents andaqueous solutions of volatile organic solvents comprising at least apredominant proportion of organic solvent in which the im-' pregnant hassubstantially less solubility as compared to the hydrophobic solvent andcontinuing the agitation until additional impregnation is effected,removing theleather from the liquid system, draining it, and drying it.

3. A method as defined in claim 2 in which the impregnant comprises apolymer of at least one monoethylenically unsaturated compound.

4. A method as defined in claim 2 in which the inipregnant comprises apolymer of at least one ester of an acid of the group consisting ofacrylic, methacrylic and itaconic acids with a higher aliphatic alcoholhaving from 8 to 30 carbon atoms.

5. A method as defined in claim 2 in which the impregnant comprises apolymer of an ester of methacrylic acid with an alcohol having from 8 to30 carbon atoms.

6. A method as defined in claim 2 in which the impregnant comprises acopolymer of cetyl methacrylate with stearyl methacrylate.

7. A method as defined in claim 2 in which the impregnant comprisestallow.

8. A method as defined in claim 2 in which the impregnant comprises along-chain isocyanate having 8 to 30 carbon atoms.

9. A method as defined in claim 2 in which the impregnant comprisesoctadecyl isocyanate.

10. A method as defined in claim 2 in which the impregnant comprises along-chain ketene having 8 to 30 carbon atoms.

11. A method as defined in claim 2 in which the impregnant comprisesoctadecyl ketene.

12. The method of impregnating leather comprising agitating the air-dryleather with 200% to l000% of, on the weight of the leather, a solutionin a volatile hydrophobic organic solvent medium of 1% to 50% on theweight of the leather of a hydrophobic impregnant until an equilibriumcondition of distribution of the impregnant etween the medium and theleather is substantially attained, then adding a sulficient amount of awater-soluble hydrophilic solvent selected from the group consisting ofvolatile organic solvents and aqueous solutions of volatile organicsolvents comprising at least a predominant proportion of organic solventin which the impregnant is insoluble, to form a system having two liquidphases and continuing the agitation until a new equilibrium condition ofdistribution between the liquid system and the leather is attainedwhereby to efiect further exhaustion of the impregnant from the solutionand further deposition of the impregnant on the leather, removing theleather from the liquid system, draining it and drying it.

13. A method as defined in claim 12 in which the water-soluble solventis added in successive portions at spaced intervals, the agitation beingcontinued after each addition until a new equilibrium condition ofdistribution between the liquid system and the leather is substantiallyattained before the next addition.

14. A method as defined in claim 12 in which the hy-v drophilic solventcomprises a water-soluble organic soivent and at least 3% by weight ofwater.

15. A method as defined in claim 12 in which the hy drophilic solventcomprises methoxyethanol.

16. A method as defined in claim 12 in which the hydrophilic solventcomprises isopropyl alcohol and 3% to 30% by weight of water.

17. A method as defined in claim 16 in which the impregnant comprises apolymer of at least one ester of an acid of the group consisting ofacrylic, methacrylic and itaconic acids with a higher aliphatic alcoholhaving from 8 to 30 carbon atoms.

V 18. 'A method as defined in claim 16 in which the'im- ReferencesCitediin theme of this pateht V pregnant comprises a water-insolublepolymer of a c'om- UNITED STATES PATENTS pmmd havmg the 2,015,943 Loges-Oct; 1, 1935 5 C Q Z 5 2,126,321, Freudenberg et a1 Aug. 9, 1938 where Ris methyl or hydrogen and A is an alkylene group 2,204,520 Walker etJune 11, 4 having from 2 to 14 carbon atoms. 2,635,055 Flgdo? P 3- 9 l19. A method as defined in claim -16 in which the 2,635,059 Cherqms pimpregnant comprisesra copolymer of cetyl methacrylate 2,694,695 BortmckV with stearyl methacrylate. 10 2:7191072 'L- P ,1

1. THE METHOD OF TREATING LEATHER COMPRISING AGITATING THE AIR-DRYLEATHER WITH A SOLUTION IN A VOLATILE HYDROPHOBIC ORGANIC SOLVENT MEDIUMOF A HYDROPHOBIC IMPREGNATE UNTIL SUBSTANTIAL IMPREGNATION IS EFFECTED,ADDING A WATERSOLUBLE HYDROPHILIC SOLVENT SELECTED FROM THE GROUPCONSISTING OF VOLATILE ORGANIC SOLVENT AND AQUEOUS SOLUTIONS OF VOLATILEORGANIC SOLVENT COMPRISING AT LEAST A PREDOMINANT PROPORTION OF ORGANICSOLVENT IN WHICH THE IMPREGNANT HAS SUBSTANTIALLY LESS SOLUBILITY ASCOMPARED TO THE HYDROPHOBIC SOLVENT WHILE CONTINUING THE AGITATION UNTILADDITIONAL IMPREGNATION IS EFFECTED, REMOVING THE LEATHER FROM THELIQUID SYSTEM, DRAINING IT, AND DRYING IT.